Solar radiation includes about 5% ultraviolet (UV) radiation, wavelength of which is between 200 nm and 400 nm. It is further classified into three regions: from 320 to 400 nm (UV-A), 290 to 320 nm (UV-B) and from 200 to 290 nm (UV -C). A large part of UV-C radiation is absorbed by the ozone layer. Scientific studies have indicated that exposure to UV-A and UV-B radiation for short period causes reddening of the skin and localized irritation, whereas continued and prolonged exposure can lead to sunburn, melanoma and formation of wrinkles. It is also reported that UV radiation causes significant damage to hair. Therefore, it is desirable to protect the skin and other keratinous substrates of the human body from the harmful effects of both, UV-A and UV-B radiation.
Various cosmetic preparations have been reported for preventing and/or protecting the skin from harmful effects of ultraviolet radiation. Numerous organic sunscreen agents capable of absorbing UV-A rays are reported in the field of cosmetics amongst which a particularly useful sunscreen is of the dibenzoylmethane class. Many UV-B sunscreens are also known and approved for safe use in personal care compositions for protection from UV-B radiation. Many cosmetic manufacturers prefer to include both UV-A and UV-B sunscreens in photoprotective compositions so as to provide protection over the entire range of UV radiation. Sun Protection Factor (SPF) is a commonly measured attribute of photoprotective compositions which indicates the protection that the skin gets from exposure to both UV-B and UV-A radiation.
Thus cosmetic manufacturers try to provide consumers with products having higher and higher SPF. One of the ways of achieving this is to incorporate high levels of UV-A and UV-B sunscreens. One disadvantage of this approach is the high cost associated with incorporation of high levels of sunscreens which are expensive. Further, there are safety and regulatory limitations on the upper limit of incorporation of these sunscreens. Sensory properties are also reported to get affected on incorporation of high levels of sunscreens. Hence, there is a problem of achieving high SPF while keeping the total amount of sunscreens in the compositions relatively low.
Various publications on more effective sunscreen compositions have been reported. US 2004/057918 (L'Oreal) discloses a photostable UV photoprotecting amount of at least one dibenzoylmethane organic sunscreen immobilized within a matrix prepared via sol-gel process from at least one silicon oxide, with at least one non-ionic surfactant and water, but in absence of any organic solvent.
U.S. Pat. No. 4,847,069 (P&G, 1989) discloses a pharmaceutical composition comprising sorbohydroxamic acid, or pharmaceutically acceptable salts thereof, and an anti-inflammatory agent, which are useful for topical application to prevent damage to skin caused by acute or chronic UV exposure. Combinations of sorbohydroxamic acid and an anti-inflammatory agent together with tocopherol sorbate and/or sun-screens are also disclosed.
WO 2008/022946 (Unilever) discloses a cosmetic composition comprising dibenzoylmethane or its derivative and p-methoxycinnamic acid or its derivative that minimizes degradation of the dibenzoylmethane when exposed to UV radiation by incorporating a combination of fatty alcohol ethoxylates and polyalkyleneglycol. The object of WO2008/022946 is to develop a composition that minimizes degradation of dibenzoylmethane UVA sunscreen when in use and exposed to sunlight (say for 30 or 60 minutes). The object of the present invention is to develop high SPF compositions i.e ones which provide high sun protection as measured at zero point in time with respect to exposure to sunlight. Thus knowledge of a composition that minimizes degradation of a UVA sunscreen when in use by exposure to UV radiation does not automatically lead one to the conclusion that this composition will exhibit high Sun Protection Factor at the initial point of exposure to the sun's rays.
Thus, while the above publications disclose certain sunscreen compositions with a few non-ionic surfactants, none of them disclose that a class of non-ionic surfactants, identified by the present inventors, when included in sunscreen compositions having low levels of organic sunscreens, provides for high SPF.
Therefore there exists a need for a personal care composition that is able to provide much higher SPF as compared to known sunscreen compositions but at low levels of sunscreen agents. It is desirable, that the enhanced SPF benefit could be achieved through synergistic interaction of commonly used ingredients, thereby giving the desired photoprotection benefits at substantially low costs.
The present applicants have been working on solving this problem and have surprisingly found that cosmetic compositions comprising dibenzoylmethane or its derivative in combination with an oil soluble UV-B sunscreen when incorporated in a sunscreen composition along with a non-ionic surfactant of a select class meeting certain HLB requirements, provide the enhanced SPF benefits when applied on the substrate of interest.
It is therefore an object of the present invention to obviate at least some drawbacks of the prior art and provide high SPF (equal to or higher than 20) photo-protective sunscreen composition.
Another object of the present invention is to achieve the above object using relatively low amounts of sunscreen agents thereby keeping costs low.